Cost model
The pool-heating cost formula, explained
Estimate the energy required to warm a pool, convert it into heater input, and price that input using your local gas, propane, or electricity rate.
Reviewed September 2, 2026 · Planning guidance, not engineering, legal, tax, or platform-account advice.
A useful pool-heat estimate starts with physics, then adds the messy operating reality: heater efficiency, weather, evaporation, runtime, covers, and the energy price on the property's bill.
1. Calculate the heat added to the water
The U.S. Energy Information Administration defines one British thermal unit as the heat needed to raise one pound of water by one degree Fahrenheit. The 8.33 factor approximates the weight of one U.S. gallon of water.
Example: warming a 15,000-gallon pool from 65°F to 82°F requires an estimated 2,124,150 Btu delivered to the water before environmental losses.
2. Adjust for the heater
A heater consumes more input energy than the water receives unless it is modeled with an efficiency or coefficient of performance (COP).
Use the manufacturer's rated output and efficiency or COP for the conditions you expect. A heat pump's performance can move materially with air temperature and humidity, so a single catalog COP is not a guarantee.
3. Convert energy into the billing unit
| Energy source | EIA conversion | Cost step |
|---|---|---|
| Natural gas | 100,000 Btu per therm | Input Btu ÷ 100,000 × $/therm |
| Propane | 91,452 Btu per gallon | Input Btu ÷ 91,452 × $/gallon |
| Electricity | 3,412 Btu per kWh | Input Btu ÷ 3,412 × $/kWh |
4. Work a simple natural-gas example
If the 15,000-gallon example uses an 84%-efficient natural-gas heater and gas costs $1.60 per therm:
- 2,124,150 thermal Btu ÷ 84% = 2,528,750 input Btu.
- 2,528,750 ÷ 100,000 = 25.2875 therms.
- 25.2875 × $1.60 = $40.46 initial heat-up energy.
That is not the whole stay cost. It excludes heat lost while the pool is held at temperature, startup behavior, weather, accessories, labor, and other booking-specific costs.
5. Model maintenance separately
Maintenance demand is not determined by pool volume and temperature rise alone. Wind, air temperature, humidity, surface area, desired water temperature, cover use, and guest behavior all matter. The U.S. Department of Energy identifies evaporation as the dominant pool-energy loss in its commercial-pool analysis and reports that properly used covers can materially reduce heating demand, with results varying by site.
For a first estimate, use a conservative daily runtime assumption. Then replace it with observed heater hours or energy use after real stays. Keep initial heat-up and maintenance as separate lines so one does not disappear inside a flat nightly guess.